Sun SX

This is the rendering engine built into the ?SPARCstation 20's memory controller.

OpenPROM name: SUNW,SX

Sun used to call this a Pixel Processor, which is exactly what it is. As far as we know this thing doesn't have much in common with conventional blitters, there are no command or coordinate registers, instead there is a bunch of registers to point the engine at memory regions ( may or may not be a CG14 VSIMM ) and a port to feed it instructions. The instruction format is unknown, but from published papers we know the SX is some sort of SIMD processor with a non-trivial number of registers, so it could likely be used to accelerate composite operations. Unfortunately it can't read instructions from memory and as far as we know it doesn't have any kind or branch instructions so we always have to feed it instructions one by one using the main CPU ( and if this is indeed the only way to feed it instructions then branching instructions don't make any sense anyway ).
So far there is no driver support for the SX in any open source operating system, drivers exist for Solaris and NEXTSTEP.